The invention relates generally to communicating voice and video information over a channel having a fixed capacity, such as a telephone communication channel.
Video conferencing systems typically transmit both voice and video information over the same channel. A portion of the channel's bandwidth is typically dedicated to voice information and the remaining bandwidth is allocated to video information.
The amount of video and voice information varies with time. For example, at certain moments in time, a person at one end of the system may be silent. Thus, if the system includes a variable capacity voice encoder, little information needs to be transmitted during such moments of silence.
Similarly, the video signal may have little or no change between frames as, for example, when all objects within the field of view are still. If the system includes a variable capacity video encoder, little information needs to be transmitted during such moments of inactivity. At the other extreme, during times of great activity, the amount of video information may exceed the channel capacity allocated to video information. Accordingly, the system transmits as much video information as possible, discarding the remainder.
Typically, the video encoder accords priority to the most noticeable features of the video signal. Thus, high priority information is transmitted first and the less noticeable low priority information is temporarily discarded if the channel lacks sufficient capacity. Accordingly, it is desirable to have available as much video bandwidth as possible.
It is therefore an object of the present invention to reduce the amount of channel bandwidth allocated to audio information whenever there is little audio information required to be sent. The remaining portion of bandwidth is allocated to video information. Thus, on average, a lower bit rate is provided for audio information and a higher bit rate is provided for video information.